Conventionally, in a semiconductor device which semiconductor element, such as an FET, passive elements, such as a thin film capacitor, etc. are placed on, for example, a printed circuit board or a metal plate and are connected, a structure where a semiconductor element is grounded is used by a via hole (VIA) provided in an inside of the semiconductor element.
In the semiconductor device which has the structure of the thinned GaAs substrate in which a GaAsFET is formed, and grounding any of a desired electrode, such as a gate on a GaAs substrate, a drain, or a source, as a semiconductor device which includes a substrate via hole which passes through the GaAs substrate from the back and reaches a desired electrode, a metal layer which is formed in the back of the GaAs substrate and contacts a desired electrode in a GaAs substrate via hole, a dielectric layer laminated on a metal layer, and a ground electrode layer formed on a dielectric layer, for example, there are some which are described in the Patent Document 1.    Patent Document 1: JP, 62-2466, B.
On the other hand, further high power and high breakdown voltage capability is required with advanced features of an inverter circuit or a switching element. Then, in recent years, as a substrate of an FET element, an SiC (silicon carbide) substrate, which a band gap and a dielectric breakdown electric field are large and has excellent physical properties, is used. This SiC substrate is the substrate material excellent also in thermal conductivity with the thermal conductivity more than metal.
When using the SiC substrate for a power device of a microwave band, it is necessary with a high increase in power to emit the heat to generate efficiently.
However, when it grounds by providing a via hole in the SiC substrate by using the above methods, there is a problem that heat conduction is obstructed in the via hole portion and the thermal conductivity which SiC has cannot be used effectively.
Moreover, in order to form a via hole in the SiC substrate, there is a problem that processes, such as patterning and etching, are required, and the via hole opening process becomes complicated.
In a semiconductor device by which a semiconductor element and peripheral circuit section, such as, a matching circuit section, a bias circuit section, a capacitor element, are placed and connected to on a substrate, an object of the present invention is to provide a semiconductor device which can ground a semiconductor element, and can make heat dissipation characteristics of a semiconductor element satisfactory, without providing a via hole into a semiconductor substrate.